Polymeric documents of value offer several benefits over their paper counterparts. In particular, polymeric banknotes can offer greatly increased durability and resistance to counterfeiting through the incorporation of security features. A requirement for polymeric banknotes is that certain physical properties are similar to the more commonly used paper banknotes. Those properties relate to tactile feel, strength, tear resistance, handling, folding, and crumple resistance.
In the past, laminates have been used for banknotes having biaxially oriented polymeric film and a non-printed window incorporate security features. However, there are several the shortcomings of banknotes based on some of the laminates. Laminate constructions primarily based on polyolefin film offer improved physical properties. Other alternatives include banknotes that incorporate outer layers of paper laminated to a polymeric core as a way to obtain paper-like properties.
Polymeric banknotes offer unique opportunities to incorporate security features that are designed to discourage counterfeiting. Many efforts relating to banknotes describe the possibility of a transparent window somewhere on the banknote, which offers a quick visual check for authenticity and is difficult to reproduce with copying techniques. Further refinements of the window include an optically variable device, such as a Moire pattern or diffraction grating, which is visible in the window. In most cases, the security feature must be added as a separate component with an additional process step.
Polymeric laminates having a large number of layers and exhibiting optically unique properties have been considered as a basis for “plastic” currency. Multilayered optical films with unique optical properties that can be used as security features on certain documents of value have been considered. Polymeric multilayer optical films have previously been made with PEN, PET, and CoPEN polymers (See for example, U.S. Pat. No. 5,882,774).
Researchers, however fail to address the physical properties required for that application. (See additional references U.S. Pat. Nos. 4,162,343, 4,937,134, 5,089,318, and U.S. Pat. No. 6,045,894.)
There would be great value in a multilayered film with optical properties that combines the physical properties required for polymeric banknotes with an inherent security feature that would be difficult to counterfeit.